It differs primarily in that it does not require webservers to support anything. Only that a user desiring to run it has somewhere to put their personal proxy.

It also differs in that it has perfect knowledge of the state of the cache on the mobile device.

It differs significantly from rsync/rproxy, as the core of those programs - negotiating file differences over a remote link - is not done.

it does not require any negotiation over the (potentially very slow) link, and also enables the proxy to potentially send other changed pages that are referred in the changes.

Other optimisations:

Comparing pages, and ensuring that any page has in fact changed before downloading, as many servers misreport pages changed when they have not.

Convert all jpegs to progressive, and initially only download the first 'scan' of the image, which is 1/8th the size or so. Allow the user to download the remainder of the file for full resolution by clicking on it.

Different profiles, depending on how the Freerunner is connected (Wifi vs. USB vs. GPRS).

Traffic-measurement especially for GPRS-connection for users with limited data-amounts (for example 200MB/month) or in areas with limited data-consumption, like on commercial wifi-aps on airports and such.

It differs primarily in that it does not require webservers to support anything. Only that a user desiring to run it has somewhere to put their personal proxy.

It also differs in that it has perfect knowledge of the state of the cache on the mobile device.

It differs significantly from rsync/rproxy, as the core of those programs - negotiating file differences over a remote link - is not done.

it does not require any negotiation over the (potentially very slow) link.

Other optimisations:

Comparing pages, and ensuring that any page has in fact changed before downloading, as many servers misreport pages changed when they have not.

Convert all jpegs to progressive, and initially only download the first 'scan' of the image, which is 1/8th the size or so. Allow the user to download the remainder of the file for full resolution by clicking on it.

Different profiles, depending on how the Freerunner is connected (Wifi vs. USB vs. GPRS).

Traffic-measurement especially for GPRS-connection for users with limited data-amounts (for example 200MB/month) or in areas with limited data-consumption, like on commercial wifi-aps on airports and such.